System and method of solids conditioning in a filtration system

ABSTRACT

A method and apparatus for conditioning the settled solids in the bottom of a wastewater filtration tank to reduce the acidification of the sludge and prevent the excessive growth of undesirable biological growth.

FIELD OF THE INVENTION

The present inventions relate to the use of cloth media filtration inthe primary filtration stage of wastewater treatment. More particularly,the present inventions relate to systems and methods for theconditioning of solids in a cloth media filtration device used forprimary or wet weather wastewater treatment.

BACKGROUND OF THE INVENTION

A flow chart of a typical wastewater treatment process is shown in FIG.1A. Included in the process is primary treatment, secondary treatmentand optional tertiary treatment. Primary treatment consists of screeningor pretreating the influent of wastewater and sending it to a primaryclarifier. The primary clarifier removes the large solids from thewastewater by settling and skims off fats and oils that float to thetop.

The effluent from the primary clarifier is transferred to the secondarytreatment process that includes further treatment using biological meansand a secondary clarifier. In some systems, the water is disinfected andthen discharged. In other systems, a tertiary treatment step is addedbefore disinfection and discharge. A popular device used in tertiaryfiltration is cloth media filtration. An example of a preferred clothmedia filtration system is known as the AquaDisk® system, which ismanufactured and sold by the assignee of this patent, Aqua-AerobicSystems, Inc. of Rockford, Ill. A variety of typical primary, secondaryand tertiary waste water treatment systems are well known to those ofskill in the art.

Clarifiers, because of the nature of their operation, require very largetanks or basins which take up a relatively large amount of space at awastewater treatment facility. In addition, and particularly at olderplants, the primary clarifier can become overloaded in storms or otherhigh flow or wet weather conditions. In such situations, older plantswould bypass the primary clarifier and simply discharge the untreatedoverflow to rivers and the like. This is referred to as a wet weatherbypass in FIG. 1A. For obvious reasons, this is unacceptable.

To solve the space and overflow issues, Aqua-Aerobic Systems pioneeredthe use of cloth media filtration, typically used in tertiary treatmentapplications, for use in the primary treatment phase of wastewatertreatment. As shown schematically in FIG. 1B, a cloth media filtrationdevice is used to replace the standard primary clarifier (see FIG. 1A).A preferred example of a cloth media filtration system used in primarytreatment to replace the primary clarifier is known as the AquaPrime®system, which is manufactured and sold by the assignee of this patent,Aqua-Aerobic Systems Inc. of Rockford, Ill. This system, when used inprimary filtration, saves space at the plant and has a higher and fasterrate of solids removal than a typical primary clarifier. In fact, it hasbeen determined that a cloth media filtration device used for primaryfiltration will require only 10%-15% of the space required by aconventional primary clarifier. In addition, because of its high solidsremoval, substantial energy and operational savings are achieved by theuse of cloth media filtration for primary treatment of wastewater.

In addition, and as set forth schematically in FIG. 1C, the preferredAquaPrime® system may also be used as a tertiary filtration system (inplace of, for example, the AquaDisk® system) and as a wet weather backup primary treatment system. In those situations, the preferred clothmedia filtration system for tertiary treatment is the AquaPrime® system.In periods of high flow and/or storm conditions, influent may be all orpartially diverted to the AquaPrime® cloth media filtration system andthen back to the primary clarifier.

The use of cloth media filtration for primary and wet weather wastewatertreatment revealed certain unique problems. For example, as the sludgebuilds-up as a result of excess detention time in the sludge hopper atthe bottom of the cloth media filtration tank, the sludge can becomeanaerobic. This can result in the acidification (fermentation) of thesludge that can reduce the pH in the lower portion or sludge hopper ofthe filtration tank. This, in turn, can lead to the development ofundesirable bacteria and other organisms like fungi. If not controlled,the undesirable biological growth can interfere with the normaloperation of the cloth filtration media and overall performance of thesystem. Such organisms can also be difficult to remove once established.In addition, the solids which contain grit, debris and other organicsare prone to compaction and can make removal and/or collection for usein other processes difficult. And, while excess sludge may be removedfrom the sludge hopper by a solids collection manifold, it is necessaryto interrupt filtration to do so. That is undesirable.

Further, microbial induced corrosion is another example of undesirablebiological growth caused by prolonged anaerobic activity in filtrationsystems. Sulfate reducing bacteria can produce localized, strong acidswhich can degrade concrete and steel tank structures. That is alsoundesirable.

The present inventions solve these and other problems associated withthe use of cloth media filtration in the primary treatment of wastewateras well as for wet weather conditions. For example, the presentinventions provide for apparatus and methods to mix (or condition) thesludge (solids) at the bottom of the filtration tank, typically usingbulk liquid and/or incoming flow which can neutralize the pH (i.e.,increase the pH) of the sludge and the overall tank to prevent thegrowth and/or build-up of fungus and undesirable bacteria. The presentinventions may also distribute oxygen throughout the tank to preventprolonged anaerobic activity from corroding the tank's surface orconcrete. In addition, the conditioning of the solids at the bottom ofthe tank can prevent excessive compaction and improve solids removal bythe solids collection manifold. The present inventions also reduce thefrequency of sludge removal and take up a smaller footprint at awastewater treatment plant.

SUMMARY OF THE INVENTION

The present inventions preserve the advantages of known cloth mediafiltration systems and methods and also provide new features andadvantages, particularly for cloth media filtration use for primarywastewater treatment.

Therefore, it is an object of the present inventions to provide a solidsconditioning apparatus and method for use with cloth media filtration inprimary wastewater treatment.

Another object of the present inventions is to neutralize (or raise) thepH of the contents of a cloth filter media filtration tank used forprimary filtration by periodically conditioning the sludge.

An additional object of the present inventions is to provide a methodand system to control the conditioning, build-up and compaction ofsolids in the cloth media filtration tank.

A further object of the present inventions is to mix or loosen thesettled solids to aid in solids removal.

Still another object of the present inventions is to provide a methodand apparatus for solids conditioning that help eliminate the growth orbuild-up of undesirable biological growth in the cloth media filtrationdevice used in primary wastewater treatment and to reduce the frequencyof solids removal or collection.

Still an additional object of the present inventions is to provide a jetmixing system near the bottom of the cloth filter media tank to conductsolids conditioning, potentially using existing backwash or solids wasteequipment (such as valves, pumps and piping).

Still a further object of the present inventions is to provide a methodand system that controls the frequency, duration and intensity of solidsconditioning in a cloth media filtration used for primary filtration.

Still yet another object of the present inventions is to improve theoverall characteristics of the wasted solids by eliminating thepreferential withdrawal of liquid due to rat-holing (short circuiting)or sludge blanket filtration thereby improving the efficiency of solidsremoval.

Still yet a further object of the present invention is to distributeoxygen throughout the tank to prevent microbial induced corrosion causedby anaerobic bacteria biofilm formation at the tank or concretesurfaces.

According to the stated and unstated objects, features and advantages ofthe present inventions, a system to condition a build-up of settledsolids or sludge from a bottom of a wastewater treatment filtration tankis provided. The system includes a sludge hopper on the bottom of thetank for collecting the sludge; a high velocity jet nozzle adjacent tothe sludge hopper, the jet nozzle in fluid communication with a solidsconditioning valve; and, a pump in fluid communication with the jetnozzle and in fluid communication with a fluid from a fluid source fromthe tank, wherein the fluid is pumped by the pump through the solidsconditioning valve and through the jet nozzle to fluidize the sludge inthe sludge hopper by the output of the jet nozzle. The system may alsoinclude an embodiment wherein the fluid source is from a sludgecollection manifold on the bottom of the sludge hopper, the sludgecollection manifold in fluid communication with a solids waste valve andsaid pump. Alternatively, the fluid source may be from a backwash shoein the tank, the backwash shoe in fluid communication with a backwashvalve and the pump. In a preferred embodiment, the jet nozzle generatesa flow velocity greater than fifteen feet per second.

A method of conditioning sludge which has settled in a sludge hopper ona bottom of a cloth medial filtration tank, the tank having a manifoldused in the removal of sludge during a sludge wasting mode and having abackwash shoe for conducting a backwash mode is also provided. Apreferred embodiment of the method of conditioning sludge includes thesteps of sensing a solids conditioning mode triggered event; waitingcompletion of the sludge wasting mode; initiating a solids conditioningmode upon the sensing of a trigger event and the completion of thesludge wasting mode; selecting a flow source for said solidsconditioning mode; conducting said solids conditioning mode using a highvelocity nozzle adjacent to the sludge hopper; and, terminating saidsolids conditioning mode after the lapse of a predetermined amount oftime. In one embodiment, the flow source for the solids conditioningmode is from said manifold. In another preferred embodiment, the flowsource for the solids conditioning mode is from the backwash shoe. Themethod provides for a trigger event, one of which is the passage of apredetermined amount of time. Another trigger event is a low pH readingin the sludge. Still another trigger event is the conduct of apredetermined amount of backwash modes. And, finally, a fourth triggerevent may be a low ORP reading in the sludge. In another embodiment, thesolids conditioning mode may be aborted based upon a sensing of a highwater level in the tank signaling the necessity to conduct a backwashmode.

Inventor's Definition of the Terms

The terms used in the claims of this patent are intended to have theirbroadest meaning consistent with the requirements of law. Wherealternative meanings are possible, the broadest meaning is intended. Allwords used in the claims are intended to be used in the normal,customary usage of grammar, the trade and the English language.

BRIEF DESCRIPTION OF THE DRAWINGS

The stated and unstated objects, features and advantages of the presentinventions (sometimes used in the singular, but not excluding theplural) will become apparent from the following descriptions anddrawings, wherein like reference numerals represent like elements in thevarious views, and in which:

FIG. 1A is a flow chart showing a typical wastewater treatment process.

FIG. 1B is a flow chart showing a typical wastewater treatment processusing cloth media filtration as part of the primary treatment process inplace of a primary clarifier.

FIG. 1C is a flow chart of a typical wastewater treatment process usingcloth media filtration for tertiary treatment as well as for primarytreatment in wet flow or overflow conditions.

FIG. 1D is a cross-sectional schematic side view of the principalcomponents of a preferred cloth media filtration system configured foruse in the primary treatment of wastewater and in overflow or wetweather conditions.

FIG. 2 is a cross-sectional schematic side view of a preferredembodiment of the present invention having solids conditioning equipmentcapable of practicing a preferred method of the present invention shownin conjunction with the preferred cloth media filtration system.

FIG. 2A is a cross-sectional schematic side view of a preferredembodiment of the present invention showing the representative valves,pump and probes connected to a PLC for control of the system, includingthe solids conditioning mode.

FIG. 3 is a flow chart of a preferred embodiment of the method andsystem of solids conditioning of the present invention.

FIG. 3A is the detailed portion of the flow chart labelled 3A in FIG. 3.

FIG. 3B is the detailed portion of the flow chart labelled 3B in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Set forth below is a description of what is currently believed to be thepreferred embodiments or best representative examples of the inventionsclaimed. Future and present alternatives and modifications to theembodiments and preferred embodiments are contemplated. Any alternativesor modifications which make insubstantial changes in function, purpose,structure or result are intended to be covered by the claims of thispatent.

As indicated, Aqua-Aerobic Systems, Inc. pioneered the use of clothmedia filtration in the primary treatment of wastewater. A preferredembodiment of such a system is known as the AquaPrime® system. Aschematic representation of the principal components of the AquaPrime®primary cloth media filtration device is shown schematically as 10 inFIG. 1D. Cloth media filtration system 10 includes a tank 11. It will beunderstood by those of skill in the art that tank 10 may be constructedwith steel or may take the form of a traditional concrete basin.

Tank 11 includes a bottom portion 12 and a top portion 13. The topportion 13 includes an inlet (not shown) and an overflow 14. A scum weir15, and an associated scum line 16 and scum valve 17 are also provided.As will be understood by those of skill in the art, the scum weir 15 isused to remove the fats and oils that float to the top of the tank. Tank11 typically has a high water level 18 and a low water level 19, thesensing of which may trigger a backwash operation. Filtering isconducted using one or more disk filter members 20 that are in fluidcommunication with a hollow center tube 20 a that discharges thefiltered influent for further processing as will be understood by thoseof skill in the art. This aspect is commonly referred to as thefiltration mode 50 (see FIG. 3A).

The cloth media filtration material is periodically cleaned bybackwashing using suction. A typical cloth media filtration backwashsystem includes a backwash shoe 21 in communication with a backwash line22 having a backwash valve 23 and an associated pump 24. A dischargeline 25 is provided. An associated discharge valve 26 may also beprovided for filtration, but is required for the solids conditioningmode of the present inventions as hereinafter described. The filteringand backwash operation are understood by those of skill in the art andmay be conducted based upon the passage of time or the sensing of a highwater level. The backwashing is commonly known as backwash mode 60 (seeFIG. 3A). Reference may also be made to the AquaDisk® (tertiary clothmedia filtration) and/or AquaPrime® (primary cloth media filtration),both by Aqua-Aerobic Systems, Inc. The cloth media filtration typicallyhas a plurality of disk filter members 20. In the preferred embodiment,each pair of disk filter members has associated backwash shoes 21,backwash line 22, backwash valves 23 and pumps 24.

In a primary treatment configuration, the bottom portion 12 of tank 11includes sloped walls 27 forming a sludge hopper 32 into which thesludge 30 and other particulates settle during the filtration process. Asludge collection manifold 28, a solids waste line 29 and a solids wastevalve 31 are also provided, all of which may be controlled by acontroller 39 (FIG. 2A). As sludge 30 accumulates during the filtrationprocess, the sludge hopper 32 is periodically emptied of sludge 30through sludge collection manifold 28, as will be understood by those ofskill in the art. This aspect is referred to as the solids waste mode70, i.e., when the settled solids are removed from the system (FIG. 3B).Pump 24 (or a plurality of pumps) acts as a pump for backwashing in thebackwashing mode 60 as well as a pump for solids waste mode 70. And, asdiscussed below, it is also used for solids conditioning mode 100.

A preferred embodiment of the solids conditioning system 40 of thepresent invention may be seen by reference to FIGS. 2 and 2A. The methodof solids conditioning as described herein, with reference to thepreferred embodiment, is referred to as the solids conditioning mode orSCM. The present inventions are described in conjunction with and whenadded to a preferred primary cloth media filtration system, i.e., theAquaPrime® system, as schematically shown in FIG. 1D. It will beunderstood by those of skill in the art that the solids conditioningsystems 40 and methods 100 of the present inventions may be used withother cloth media filtration systems configured for use in primarywastewater treatment. It will also be understood that the presentinventions are also applicable to non-primary wastewater treatmentoperation of a cloth media filtration system.

The preferred solids conditioning system of the present inventions isshown generally as 40 in FIGS. 2 and 2A. The principal componentsinclude a high velocity jet nozzle 42, a solids conditioning line 44 andsolids conditioning valve 46. Jet nozzle 42 is located in the bottomportion 12 of tank 11 and within or adjacent to sludge hopper 32. Likethe backwash components 20, 20 a, 21, 22 and 23, there is typically asolids conditioning system 40 associated with each pair of disk filtermembers 20. This is because, in the preferred embodiment, solidsconditioning system 40 preferably may use the backwash or sludge removalcomponents during SCM operation as hereinafter described. This increasesflexibility for sludge conditioning and saves costs. It will beunderstood by those of skill in the art, however, that solidsconditioning system 40 may be configured with its own pump 24 and otherselected components. In a preferred embodiment, jet nozzle 42 isdesigned to generate a velocity of at least ten feet per second, andpreferably a velocity greater than fifteen feet per second, toadequately induce the desired agitation and fluidization to the settledsludge 30.

One or more probes 35 are situated within sludge hopper 32. In apreferred embodiment, one probe 35 is a pH sensor and one probe 35 is anORP sensor. As hereinafter described, both sensors are not required andother sensors may be included. Probe 35 is electrically connected 36 toa PLC 38 which is part of a controller 39. Similarly, solidsconditioning pump 24, valve 46, discharge valve 26, backwash valve 23and solid waste valve 31 are also electronically connected 36 to PLC 38.In this manner, the various processes, including solids conditioningmode, may be electronically controlled as hereinafter described. It willbe understood by those of skill in the art that the electricalconnection 36 to PLC 38 of the various components may be wired,wireless, WiFi and/or Bluetooth and the like.

As shown in FIG. 3A, the filtration mode 50 is the standard or defaultmode of operation of cloth filter media filtration system 10. As will beunderstood by those of skill in the art, the filtration mode 50 is themain mode and is in operation approximately 95% of the time. Duringfiltration 50, the cloth filter media gradually becomes clogged withdeposited solids. As a result, the fluid level in tank 11 reaches itshigh water level 18. At this point, a backwash mode or operation 60 isconducted. In addition to the initiating of a backwash mode 60 upon thehigh water level 18 situation, backwashing mode 60 may occur based uponthe passage of time using a timer 37 as part of controller 39. Theinitiation and operation of the backwash mode 60 is well known topersons of ordinary skill in the art.

Another mode of operation is the solids waste mode 70. As the heaviersolids 30 settle in sludge hopper 32, they are removed on a periodicbasis. In general, and as will be understood by those of skill in theart, to conduct the solids waste mode 70, solids waste valve 31 andwaste discharge or discharge valve 26 are opened. Pump 24 is activatedand sludge 30 is removed through sludge collection manifold 28 anddischarged via discharge line 25 to waste handling facilities orotherwise disposed of. Like the other modes of operation, solids wastemode 70 may be electronically controlled via controller 39.

During the filtration mode 50, the solids 30 have a tendency to settleand compact. This can lead to poor or incomplete solids removal and canalso lead to acidification of the sludge 30 or the growth of undesirableorganisms. The solids conditioning mode or SCM 100 of the presentinvention provides the energy necessary to fluidize the solids or sludge30 to optimize the solids waste mode 70 and help prevent acidificationof sludge 30 and the build-up of undesirable organisms. The SCM 100 isused in conjunction with the solids conditioning system 40.

In a preferred embodiment, SCM 100 may be initiated upon the occurrenceof one of four triggered events. Specifically, SCM 100 may be initiatedby the lapse of time 102 of an SCM timer 37. In typical plants andoperations, this time may be between two to four hours. It will beunderstood by those of skill in the art that the amount of time beforean SCM mode 100 may be based upon the particular plant and loadingrequirements. As shown in FIG. 3A, if the set length of time isexceeded, the SCM mode 100 is initiated after the next solids waste mode70 at SCM pending mode 110 as hereinafter described. Again, the sensingof trigger events and operation of valves and the like are preferablycontrolled by controller 39.

If the time 102 has not been exceeded, SCM mode 100 may be initiatedwhen anaerobic conditions or a low pH is sensed in the sludge 30 byprobes 35 located in sludge hopper 32. If the low pH condition 104 issensed, the system goes into the SCM pending mode 110. A typical low pHsetting, as will be understood by those of skill in the art, is when thepH of sludge 30 is less than 6.0 or 6.5. Other set points may be chosenby the plant operator.

A third condition that may be used to trigger a solids condition mode100 is when the backwash count 106 since the last prior SCM mode 100 wasconducted. This is because solids loading (i.e., the deposition ofsolids 30 in sludge hopper 32) is directly related to the frequency ofthe backwash operation 60. If the solids level 30 drops, the frequencyof backwash 60 is reduced. If the solids level 30 raises, the frequencyof backwash operation 60 increases. Thus, in a preferred embodiment, theSCM mode 100 may be triggered by backwash mode 60 frequency. This typeof trigger may be desirable in applications which occasionallyexperience very heavy solids loading, but the system does not include apH 35 or ORP 35 sensor. As shown in FIG. 3A, if the backwash count 106has been exceeded, then the system goes into SCM pending mode 110.

A fourth trigger for the initiation of the SCM mode 100 is reaching alow oxygen reduction potential 108 or ORP in sludge 30. The ORP level ofsludge 30 is sensed by probes 35 and sent to the controller 39. Forexample, a low ORP level could be negative 100-200. If the set ORP levelis reached, the system goes into SCM pending mode 110.

SCM pending mode 110 is used to delay SCM mode 100 until the mostopportune stage. In particular, when one of the four above describedtriggers, i.e., 102, 104, 106 or 108, occurs, the system waits toconduct the SCM mode 100 until after a solids waste removal mode 70. Forexample, a solids waste mode occurs every three to four backwash modes60 (similar to the backwash count trigger discussed above). And, in atypical plant, each filter member 20 is backwashed approximately everyten to fifteen minutes, although it will be understood by those of skillin the art that backwash mode 60 and solids waste mode 70 can occur moreor less frequently. Upon completion of the solids waste mode 70, thesolids conditioning mode 100 is initiated.

The steps and operation of a preferred embodiment of solids conditioningmode 100 are best seen by reference to FIGS. 2, 2A and 3. Whenconducting the SCM mode 100, solids conditioning valve 46 is opened 112such that fluid may flow through solids conditioning line 44 and throughhigh velocity jet nozzle 42. Also, the waste discharge valve 26 isclosed 114. At this point, and depending upon conditions, the flowsource 116 for solids conditioning mode 100 may come from one of twosources. This ability to choose the flow source 116 enhances flexibilityof the system. It is possible, but not a normal mode of operation, thatboth sources may be simultaneously used for the SCM mode 100. Forexample, if a filter 20 becomes so blocked with solids that it cannot beproperly backwashed and the solids conditioning manifold 30 is partiallyor fully blocked, the operator could use both sources to bring thesystem back to normal.

In the primary mode of operation, the flow source 116 for the SCM 100 isthe solids waste collection manifold 28. Solids waste valve 31 is opened118. As a result, fluid may be drawn through sludge collection manifold28 through solids waste line 29 via activation 120 of pump 24 throughsolids conditioning line 44 and out high velocity jet nozzle 42.

Alternatively, in a preferred embodiment, the primary flow source 116may come from the backwash line 22. This flow source 116 option istypically selected if there is a high quantity of debris in the system.In this operation, fluid enters backwash valve 23 which is opened 117and center tube 20 a is rotated 119. Fluid then flows through backwashshoe 21 into backwash line 22 through activation of pump 24. This fluidthen flows through solids conditioning line 44 and out high velocity jetnozzle 42.

In the preferred embodiment, there is a check 122 to determine if theSCM 100 should be aborted in the situation where there is too muchinfluent flow to the cloth filter media system 10. This occurs when ahigh water level 18 is reached in tank 10, making it necessary toconduct the backwash mode 60 so the system 10 may perform normally. Ifno such situation exists, the SCM 100 is completed upon the expirationof the predetermined time 124. As will be understood by those of skillin the art, the SCM 100 time is determined by the operation based uponthe condition of the treatment facility and trial and error. An SCM 100time of one to two minutes is typical.

Upon completion of the SCM 100, pump 24 is stopped 220. Then, dependingupon the flow source 216, the appropriate valves are closed. If solidswaste manifold 28 was the source of the flow 216, the solids waste valve31 is closed 218. If the flow source 216 is the backwash line 22, thecenter tube 209 is stopped 219 and backwash valve 23 is closed.Regardless of the flow source 216, solids conditioning valve 46 isclosed 212 and the SCM 100 is ended or completed 200.

The above description is not intended to limit the meaning of the wordsused in or the scope of the following claims that define the invention.Rather, it is contemplated that future modifications in structure,function or result will exist that are not substantial changes and thatall such insubstantial changes in what is claimed are intended to becovered by the claims. Thus, while preferred embodiments of the presentsystem and method inventions have been illustrated and described, itwill be understood that changes and modifications can be made withoutdeparting from the claimed invention. In addition, although the term“claimed invention” or “present invention” is sometimes used herein inthe singular, it will be understood that there are a plurality ofinventions as described and claimed.

Various features of the present inventions are set forth in thefollowing claims.

1. A system to condition a build-up of settled solids or sludge from abottom of a wastewater treatment filtration tank comprising: a sludgehopper on the bottom of said tank for collecting said sludge; a sludgecollection manifold extending along the bottom of the length of thesludge hopper, the sludge collection manifold in fluid communicationwith a solids waste line, a solids waste valve and a pump; a highvelocity jet nozzle within the sludge hopper, the jet nozzle in fluidcommunication with a solids conditioning line and a solids conditioningvalve, said solids conditioning line separate from said solids wasteline; and, said pump in fluid communication with the solids conditioningline and the jet nozzle and in fluid communication with a fluid from afluid source from said tank, wherein said fluid is pumped by said pumpthrough the solids conditioning valve and through the jet nozzle tofluidize the sludge in said sludge hopper by the output of the jetnozzle and to introduce oxygen into the sludge.
 2. (canceled)
 3. Thesystem of claim 1 wherein said fluid source is from a backwash shoe insaid tank, said backwash shoe in fluid communication with a backwashvalve and said pump.
 4. The system of claim 1 wherein said jet nozzlegenerates a flow velocity greater than fifteen feet per second. 5.-12.(canceled)
 13. The system of claim 1 including a controller having a PLCto control the initiation of conditioning of the settled solids; and, atleast one probe in the sludge hopper, the at least one probe incommunication with the PLC of the controller to determine the initiationand duration of the solids conditioning mode.
 14. The system of claim 1wherein said jet nozzle generates a flow velocity between one andfifteen feet per second.